Multicast Only Fast Re-Route (MoFRR) is an enhancement to multicast routing protocols such as Protocol Independent Multicast (PIM), Multi-point Label Distribution Protocol (mLDP) and so on. An implementation of MoFRR is described in more detail in Internet Engineering Task Force (IETF) Network Working Group draft document dated Mar. 9, 2012 and entitled “draft-karan-mofrr-02” (hereinafter “Karan”). Briefly, on a PIM enabled edge router having multicast receivers, MoFRR logic determines a primary Upstream Multicast Hop (UMH) and a secondary UMH and joins the tree via both simultaneously. Data packets are received over the primary and secondary paths. Only the packets from the primary UMH are accepted and forwarded down the tree, the packets from the secondary UMH are discarded. The UMH determination is different for PIM and mLDP.
When a failure is detected on the path to the primary UMH, a repair occurs by changing the secondary UMH into the primary and the primary into the secondary. Since the repair is local it is performed very quickly, thereby greatly improving convergence times in the event of node or link failures on the path to the primary UMH.
Unfortunately, when a link or node on the path towards the multicast source is restored, normal PIM or mLDP functions may result in a traffic loss.